Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
1998-08-25
2001-06-19
Shah, Kamini (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C702S069000, C702S071000, C073S602000, C324S076110
Reexamination Certificate
active
06249749
ABSTRACT:
BACKGROUND OF THE INVENTION
This application is related to commonly owned, copending U.S. application Ser. No. 09/140,071, entitled “Method and Apparatus for Identifying Sound in a Composite Sound Signal”, which was filed concurrently herewith.
The present invention relates in general to separating impulsive and non-impulsive signal components within a time-domain signal, and more specifically to using wavelet transforms and sorting of wavelet coefficient sets to separate impulsive components from non-impulsive components of a time-domain signal.
Time-domain signals or waveforms may often include impulsive and non-impulsive components even though only one of these components may be of interest. For example, in either wireless or wired transmission of electrical or electromagnetic signals, interfering signals and background noise contaminate the signal as it travels through the wireless or wired transmission channel. The transmitted signal contains information, and therefore has primarily an impulsive character. The interference and background noise tends to be random and broadband, and therefore has primarily a non-impulsive character. After transmission, it would be desirable to separate the components so that the additive noise can be removed.
In other applications, sound waves may be converted to electrical signals for transmission or for the purpose of analyzing the sound to determine conditions that created the sound. If the sound is a voice intended for transmission, the picked-up sound may include an impulsive voice component and a non-impulsive background noise component. If the picked-up sound is created by operation of a machine or other environmental noise, the nature of the impulsive and/or non-impulsive sound components can be analyzed to identify specific noise sources or to diagnose or troubleshoot fault conditions of the machine, for example.
Prior art attempts to reduce unwanted noise and interference most often treat a signal as though the impulsive and non-impulsive components occupy different frequency bands. Thus, lowpass, highpass, and bandpass filtering have been used to try to remove an undesired component. However, significant portions of the components often share the same frequencies. Furthermore, these frequency bands of interest are not known or easily determined. Therefore, frequency filtering is unable to separate the components sufficiently for many purposes. Fourier analysis and various Fourier-based frequency-domain techniques have also been used in attempts to reduce undesired noise components, but these techniques also cannot separate components which share the same frequencies.
More recently, wavelet analysis has been used to de-noise signals. Wavelet transforms are similar in some ways to Fourier transforms, but differ in that the signal decomposition is done using a wavelet basis function over the plurality of time-versus-frequency spans, each span having a different scale. In a discrete wavelet transform, the decomposed input signal is represented by a plurality of wavelet coefficient sets, each set corresponding to a respective time-versus-frequency span. De-noising signals using wavelet analysis has been done in the prior art by adjusting the wavelet coefficient sets by thresholding and shrinking the wavelet coefficients prior to recovering a time-domain signal via an inverse wavelet transform. However, this technique has not resulted in the desired signals being separated to the degree necessary for many applications.
SUMMARY OF THE INVENTION
The present invention has the advantage of accurately separating impulsive and non-impulsive signal components in an adaptive and efficient manner.
In one aspect of the invention, a method of separating impulsive and non-impulsive signal components in a time-domain signal is comprised of decomposing the time-domain signal using a wavelet transform to produce a plurality of sets of wavelet coefficients. Each set of wavelet coefficients corresponds to a respective time-versus-frequency span. A respective statistical parameter is determined for each set of wavelet coefficients. A new time-domain signal is re-synthesized using an inverse wavelet transform applied to selected ones of the sets of wavelet coefficients. The selected ones are selected in response to the respective statistical parameters.
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Hsueh Keng D.
Lei Sheau-Fang
Tran Vy
Ford Global Technologies Inc.
Mollon Mark L.
Shah Kamini
Vo Hien
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